This invention relates to enhanced oil recovery. More specifically, this invention relates to a process of enhancing oil recovery with steam injection.
Many hydrocarbons are too thick to be recovered from subterranean petroleum containing formations without assistance. These hydrocarbons are either the residual oil left in a depleted reservoir or virgin heavy hydrocarbons. These heavy hydrocarbons can be recovered through the use of steam drives which heat the formation, lower the viscosity of the hydrocarbons,, and enhance the flow of the hydrocarbons toward a production well. However, after initial steam injection breakthrough at the production well, the steam injection preferentially follows the path of the breakthrough. Thus, the total amount of the formation that is swept by the steam injection is limited. Commercial surfactants, such as Thermophoam BW-D.RTM., a product of the FarBest Company, and Stepanflo 30.RTM., a product of the Stepan Company, have been injected along with steam to create a steam-foam flood. The surfactants form a foam that inhibits the flow of the steam into that portion of the formation containing only residual oil saturation. Residual oil saturation is defined as the immobile oil remaining in that portion of the reservoir swept steam. This forces the steam to drive the recoverable hydrocarbons from the less depleted portions of the reservoir toward the production well(s).
To maximize the extraction of hydrocarbons from a formation, it would be highly desirable to have superior foaming surfactants which inhibit the flow of steam in a steam zone containing only residual oil saturation. Furthermore, it would be desirable to have the surfactants in a steam foam recovery process which inhibit the flow of the steam in the zone which contains only the residual oil and enhance the flow of steam in the zone which contains the recoverable hydrocarbons. However, it is desirable not to have the flow of the recoverable hydrocarbons inhibited in the steam zone having an oil saturation greater than the residual oil saturation.